Add Bookmarking (Local to device)

Changelog-Added: Bookmarking
Closes: #649

damus/Models/BookmarksManager.swift

@@ -0,0 +1,50 @@
+//
+//  BookmarksManager.swift
+//  damus
+//
+//  Created by Joel Klabo on 2/18/23.
+//
+
+import Foundation
+
+class BookmarksManager {
+    
+    private let userDefaults = UserDefaults.standard
+    private let pubkey: String
+    
+    init(pubkey: String) {
+        self.pubkey = pubkey
+    }
+    
+    var bookmarks: [String] {
+        get {
+            return userDefaults.stringArray(forKey: storageKey()) ?? []
+        }
+        set {
+            let uniqueBookmarks = Array(Set(newValue))
+            if uniqueBookmarks != bookmarks {
+                userDefaults.set(uniqueBookmarks, forKey: storageKey())
+            }
+        }
+    }
+    
+    func isBookmarked(_ string: String) -> Bool {
+        return bookmarks.contains(string)
+    }
+    
+    func updateBookmark(_ string: String) {
+        if isBookmarked(string) {
+            bookmarks = bookmarks.filter { $0 != string }
+        } else {
+            bookmarks.append(string)
+        }
+    }
+    
+    func clearAll() {
+        bookmarks = []
+    }
+    
+    private func storageKey() -> String {
+        pk_setting_key(pubkey, key: "bookmarks")
+    }
+}